Image magnifier

ABSTRACT

An image magnifier and intensifier has a vacuum flask upon one end of which lies a photo-cathode. The image-producing ray bundle releases at its surface electrons depending upon the intensity distribution in its cross-section. They are represented electronically-optically at high acceleration voltage upon a screen located upon the other end of the flask. The photo-cathode represents a calotte having a curvature which differs from the middle to the edge and an opening directed toward the screen. The invention is particularly characterized in that the cross-section of the cathode has a meridianal curvature radius which increases greater than linearly from the center to the edge.

United States Paten 1191 1111 3,784,830 Schwierz et al. 1 Jan. 8, 1974 [54] IMAGE MAGNIFIER 3,417,242 12/1968 Windebank 250 213 VT 3,57 7 l l [75] Inventors: Giinter Schwierz, Erlangen; Peter 7 02 5/ 97 Szegho 250/213 VT Wulff, Frauenaurach, both of 4 Germany Primary Examzner-James W. Lawrence Assistant ExaminerD. C. Nelms [73] Assignee: Siemens Aktiengesellschait, v Alexander Scher Erlangen, Germany [22] Filed: Oct. 4, 1971 57 ABSTRACT [21] Appl' An image magnifier and intensifier has a vacuum flask upon one end of which lies a photo-cathode. The im- [30] F i A li ti P i it D t age-producing ray bundle releases at its surface elec- Oct. 7 1970 Germany P 20 49 127.4 fi the intensity distribution in its cross-section. They are represented electronically- 52 us. c1 250/213 v'r, 313/65 Optically at high acceleration Voltage "P a Screen 51 rm. (:1. H01j39/12 located upon the other end of the flask- The P [58] Field of Search 250/207 213 R 213 VT, cathode represents a calotte having a curvature which 250/833 R 833 H 71.5. 5 108 64 differs from the middle to the edge and an opening di- 66 94 rected toward the screen. The invention is particularly characterized in that the cross-section of the cathode [56] References Cited has a meridianal curvature radius which increases UNITED STATES PATENTS greater than linearly from the center to the edge. 3,683,194 8/1972 2 Claims, 2 Drawing Figures Levin 313/65 PATENTEBJAN 8 m4 [erg M 2% r P AT T OfLME'dS llMAGlE MAGNllFKlEllR This invention relates to an image magnifier and intensifier with a vacuum flash upon one end of which lies a photocathode. The image-producing ray bundle releases at its surface electrons depending upon the intensity distribution at its cross-section which are represented electronically optically at high acceleration voltage upon a screen located at the other end of the flask. The photo-cathode represents a calotte having a curvature which differs from the middle to the edge, while its opening is directed toward the screen.

Image magnifiers of this type are used to provide increased visibility of ray image s, particularly in medical X-ray diagnosis, so as to obtainbright X-ray images.

Known image magnifiers with electronic-optical imagery employ spherical calottes. They produce image surfaces which are also curved (image field curvature). However, this image field curvature makes to a great extent ineffective an often good impression of the elements of the image producing system of an image magnifier (for example, upon a screen or screens) when the usual flat outlet screen is used. On the other hand these screens must be flat in order to be able to observe without difficulty an image which is increased by use of a magnifying glass or to provide a flat ingoing image for image chains (remote vision), although the outgoing image has been diminished in known manner electronically optically for intensification etc. In that case the best impression due to the curvature of the image is produced upon a very narrow zone concentrical to the image magnifying axis. Even this cathode having a curvature radius which is different, namely diminishing from the middle to the edge, was not found to be satisfactory, since it does not producea flat image.

, An object of the present invention is to improve the described prior art constructions.

Other objects will become apparent in the course of the following specification.

In accordance with the present invention the impression of an outgoing image of an image magnifier having a flat outlet screen is improved by the flattening of the image surface in that the cross-section of the cathode calotte has a meridianal radius which increases greater than linearly from the center to the edge. This means that the curvature extends in such manner that in each point it is above a tangent applied thereon. The increase of the radius does not have to be completely uniform. It is only of importance that this rule of the present invention should be kept in relation to the entire meridianal cross-section. The advantageous effect of the present invention can be explained in that in the case of the new shape of the cathode the electron bundles emerging from thecentral zones of the cathode are stronger focussed than those coming from the zones at the edge, so that the length of the image producing electron bundles is adapted to each other with respect to flat representation. Furthermore, cushion-like distortions appearing in existing constructions, namely when using a spheric calotte, are greatly diminished by the present invention, since the angle between the normal line to the cathode surfaces at points of the edge zone and the image magnifying axis is smaller than in the case of spheric calottes. This diminishes distortions due to the more effective projection of rays upon the inlet of the image magnifier, consequently upon the photo-cathode and due to a smaller inclination of the electron bundle emerging close to the edge of the cathode, as compared to a spherical cathode.

in accordance with a preferred embodiment of the present invention consideration is taken of the fact that at least in medical diagnosis mainly only those image magnifiers are suitable to which the following formula can be applied:

Here L is the length of the image magnifying system, namely, the distance of the photo-cathode from the outlet screen of the system; R is the radius of the electrode following the cathode in the direction of the anode. lmage magnifiers having a larger value than R/L would hardly produce useable images due to very strong impressions. A smaller value of R/L contradicts the known requirement that image magnifiers should be as short as possible. Furthermore, only a part of R need be used for the image since details of importance particularly for the medical diagnosis as a rule can be brought into an image field which can be placed in the middle zone of the image magnifier inlet. For a suitable compromise which also takes into consideration the appearance of edge disturbances, it suffices to keep the image flat upon a width which corresponds to the equatron:

whereby it is the radius of the range of the photocathode for which the described method provides with security a substantially flat image surface upon the outlet screen. Then the following pair of formulas are produced for the curvature of the calotte carrying the photo-cathode:

Here 0'0 is the meridianal radius in the center of the cathode and (Th that at the distance h; correspondingly 0'h/2 is the radius at a distance h/2 from the center.

The shape of the photo-cathode can be provided, for example, by a carrier upon which the known layers are applied. Self-carrying layers can be brought by pressure into the shape of the present invention; When visible light is used for magnifying the carrier should be transparent and consist, for example, of glass. For use in X-ray image magnifiers a carrier can be also used which consists of an opaque substance transmitting X- rays, such as, for example, the metalsaluminum and beryllium or ceramic materials.

The invention will appear more clearly'from the following detailed description when taken in connection with the accompanying drawing showing by way of example only, a preferred embodiment of the inventive idea. In the drawing:

FIG. 1 is a diagrammatic section through an elec tronic X-ray magnifier constructed in accordance with the present invention.

FIG. 2 is a diagram illustrating the arrangement and structure of its electrodes and screens.

FIG. 1 shows a vacuum tight glass flask 1 of the image magnifier. In the flask starting from the inlet window 2 are arranged the cathode 4, the image producing electrodes 5 and 6 as well as the anode 7. The rear part 3 of the flask 11 also has at the outlet window 8 the outlet screen 9. The cathode 4 includes, as is known, a carrier 10 consisting of aluminum sheets 0.5 mm. thick and the illuminating screen. 11 which is applied thereon and which contains in addition to binding means zinc sulfide activated with silver; it carries with an intermediate layer the photocathode layer 12 which it steamed thereon and which contains antimony and caesium. The outlet illuminating screen 9 is flat and consists in known manner of an aluminum layer 13 which is steamed upon the illuminating layer 14 containing zinc sulfide and which lies upon a carrier 15 of glass which is 0.3 mm. thick. A electrical potential is applied in a well known manner which is therefore not illustrated, upon the cathode 4, the anode 7 as well as the electrodes 4 to 6, which produces a voltage difference of 25 kV between the cathode 4 and the anode 7. Then between the cathode 4 and the first electrode there is a voltage difference of 200 V., for the third electrode 6 there is one of l,200V., while the residue is to the anode 7.

FIG. 2, as compared to FIG. 1, shows on a larger scale the electrodes 4 to 7. It also shows the distances h, M2 and R from the center of the cathode 4, namely, the longitudinal axis of the image magnifier. There is also shown the length L of the system, which is the distance between the cathode 4 and the screen 9, as well as the diameter S of the flattened outgoing image. The photo-cathode 17 which is known in the prior art, is shown by a broken line, its cathode surface lying upon a spheric calotte. In the case of a spherical calotte a perpendicular line 18 reaches the point having the distance h from the center upon the calotte which extends steeper inwardly than the line 19 to the corresponding point of the cathode 4 of the present invention. Thus the deviation of the electron ray 20 shown by a broken line is a substantial one with respect to the line indicated as 21. In the case of image production of the present invention this results in a diminution of distortion and of vignette forming, namely in a drop in intensity toward the edge. Comparative measurements which were actually carried out, have shown that this drop in the field S is diminished by at least 50 percent as compared with outlet screens of image magnifiers with known photocathodes of spherical calotte shape.

What is claimed is:

1. An image magnifier, comprising a vacuum flask, a photo-cathode located within said flask adjacent one end thereof, and an illuminating screen carried by the other end of said flask, said photo-cathode having an opening directed toward said screen and being a calotte with a curvature which differs from the middle to the edge, said photo-cathode being characterized by a cross-section having a meridianial curvature radius which increases greater than linearly from the center to the edge.

2. An image magnifier in accordance with claim 1, further having an electrode connected with said photocathode and an anode connected with said screen, said electrode following said photo-cathode in the direction of said anode the construction of the image magnifier being characterized by the following formulas:

as well as wherein L is the length of the image magnifier, namely, the distance between said photo-cathode and said screen; R is the radius of said electrode; h is the radius of that range of the photocathode which is to have a flat imate; 00 is the meridianal curvature radius of the photo-cathode in the longitudinal axis of the image magnifier, o'h is the meridianal curvature radius of the cathode at a distance h from the longitudinal axis and (Th/2 that at a half distance h. 

1. An image magnifier, comprising a vacuum flask, a photocathode located within said flask adjacent one end thereof, and an illuminating screen carried by the other end of said flask, said photo-cathode having an opening directed toward said screen and being a calotte with a curvature which differs from the middle to the edge, said photo-cathode being characterized by a cross-section having a meridianial curvature radius which increases greater than linearly from the center to the edge.
 2. An image magnifier in accordance with claim 1, further having an electrode connected with said photo-cathode and an anode connected with said screen, said electrode following said photo-cathode in the direction of said anode the construction of the image magnifier being characterized by the following formulas: 1/6 <R/L< 1/2 , and h ( 1/2 ) R, as well as 0.7 < sigma o/ sigma h/2 < 0.95, 0.2 < sigma h/2- sigma o/ sigma h -h/2<0.4, wherein L is the length of the image magnifier, namely, the distance between said photo-cathode and said screen; R is the radius of said electrode; h is the radius of that range of the photocathode which is to have a flat imate; sigma o is the meridianal curvature radius of the photo-cathode in the longitudinal axis of the image magnifier, sigma h is the meridianal curvature radius of the cathode at a distance h from the longitudinal axis and sigma h/2 that at a half distance h. 